1. Field of the Invention
The field of art to which this invention pertains is pull cable operating levers and, more specifically, overcenter toggle-type, pull cable operating levers.
2. Description of the Related Art
The overcenter toggle-type, pull cable operating lever, as described in U.S. Pat. No. 2,464,096, is commonly used to operate vehicle parking brakes and other mechanisms actuated by a pull cable. The outer sheath of a coaxial pull cable is attached to the frame of the operating lever at one end and the frame of the vehicle at the other. The movable inner cable is attached to a brake shoe actuation mechanism in the vehicle's brake assembly and, at the other end, to a movable cable slide, guided in the frame of the operating lever assembly. A link connects the movable cable slide to a hand lever which is pivotally attached to the frame of the operating lever assembly. When the vehicle operator moves the hand lever from the "released" to the "applied" position, the movable cable slide is displaced drawing the inner cable through the outer sheath applying the brake. As the hand lever is rotated toward the "applied" position, the line connecting the points of attachment of the link rotates toward and then to the opposite side of the hand lever pivot. The mechanism goes "overcenter" causing the force exerted by the brake cable to urge or toggle the hand lever to the "applied" position. The hand lever will remain in the "applied" position until sufficient force is applied to the hand lever to move the mechanism "overcenter" in the direction of the "brake released" position.
The prior art overcenter toggle type, pull cable operating lever provides a simple and reliable means of mechanically applying a brake or other pull cable actuated device. The operator can, with reasonable force, produce adequate cable displacement and force for most applications. Maximum cable displacement is a function the distance from the hand lever pivot to the link attachment point and is maximized when the lever rotates 90 degrees. The mechanical advantage of the lever, a function of the ratio of the distances from the hand lever pivot to the point of attachment of the link and point of application of force by the operator's hand, varies throughout the range of hand lever motion, but reaches its maximum as the mechanism goes "overcenter." If required by the application, cable displacement can be increased by lengthening the distance from the hand lever pivot to the link attachment point. However, increasing displacement or reducing operator hand force requires lengthening the hand lever to maintain or increase the mechanical advantage of the hand lever. A longer hand lever requires additional motion and exertion by the vehicle operator and may make it difficult to position the operating lever assembly in the operator's station.